There has been a continual need for sintering nonoxide ceramics efficiently, particularly those that are suitable for high-hardness and high-temperature applications, such as are required for drill and tool bits and for ceramic armor. Boron carbide is an excellent lightweight material for ceramic armor and high-wear applications. However, the material does not sinter well, requiring temperatures of 2000.degree. C. or higher for densification with or without hotpressing. Microwave sintering has shown to be applicable for sintering the material, but the thermal insulating material cannot be yttria grit unless significant contamination by an yttrium-containing phase is acceptable.